This invention relates to bucket elevators. More specifically, the invention concerns a novel drive mechanism for a bucket elevator.
Bucket elevators typically are comprised of vertical steel, aluminum or wooden housings divided into three sections: a boot section, sometimes situated below around in a boot pit, in which a boot pulled is mounted; a bucket elevator casing, extending upwardly from the boot section; and a discharge section, at the top of he elevator, in which a head pulley is mounted. A flexible belt extends through the bucket elevator casing and is entrained about the two pulleys. On the outer surface of the belt are buckets which lift granular bulk materials, for example, grain, from an inlet near the boot pulley to a discharge outlet near the head pulley, where it is deposited into a suitable storage facility or takeaway device.
The prior art bucket elevator includes a take up mechanism which slides the boot pulley vertically in the boot housing to take up any slack in the downwardly moving belt strand when the bucket elevator is started and begins to lift a load.
Prior to this invention, the belt and buckets (cups) were moved by a primary drive arrangement connected to the head pulley, located generally between 50 and 250 feet above ground level. This drive arrangement comprised an electric motor connected through a flexible or fluid coupling to a gear reduction unit. The gear reduction unit, in turn, was connected, through a flexible coupling or chain and sprocket reduction, to the head pulley shaft. To move the belt and buckets slowly for damage inspection purposes, a smaller, secondary creep drive arrangement was connected to the head pulley near the larger primary drive
This invention deals with a hydraulic drive for the boot pulley of a bucket elevator, consolidating the prior primary and creep drives and take-up features into one arrangement. The invention also eliminates the heavy, complicated, hard to reach and service drive arrangement at the head end of the bucket elevator.
Driving bucket elevators at the boot pulley has never been attempted because boot pits are generally below ground and subject to moisture and material spillages. Boot pits are also crowded with equipment and not easily accessible for maintenance or replacements. Motors, switches and electrical controls at such a location could provide a possible ignition source for a dust explosion. A boot pulley drive has also never been attempted because no one has been able to establish the correct formulas or mechanical equipment to provide enough tension on the boot pulley to prevent belt slippage against the boot pulley. This slippage is to be avoided because it is also a possible ignition source for a dust explosion within the housing of the bucket elevator.
Because the head pulley was the drive pulley on prior bucket elevators, the weight of the buckets filled with granular material provided the necessary tension and friction on the head pulley to minimize slippage between the belt and the head pulley This tension was generally augmented with a counter weight or screw take up on the boot pulley. Mounting of the drive arrangement atop the bucket elevator, however, increased the construction costs of the bucket elevator and rendered the drive equipment relatively inaccessible for service and replacement Although highly unlikely, this prior art drive scheme when used in a grain elevator with unclassified electrical components, still could be a possible ignition source for explosions in the dust laden environment of a grain elevator.
Recently, a separate tensioning mechanism for bucket elevators has been introduced. The tensioning mechanism improved belt slippage problems while centering the belt on the boot pulley. This tensioning mechanism is shown in U.S. Pat. No. 4,354,595 to Reynolds. The bucket elevator electric drive arrangement disclosed in that patent was still mounted at the top of the bucket elevator and was difficult to service.
This invention overcomes the foregoing problems of difficult construction, limited access for service and the likelihood of explosions due to the drive mechanisms, by the provision of a hydraulic drive mechanism for the boot pulley of a bucket elevator. The drive mechanism comprises a hydraulic motor mounted within the boot pulley. The hydraulic motor is fluidically connected to a drive pump situated in an easily accessible area outside the boot pit, preferably at ground level away from the bucket elevator. The pump is driven by an electric motor situated close to the drive pump. Another electric motor is connected to a hydraulic drive which maintains proper tension on the belt to prevent belt slippage and to center the belt on the boot pulley.